Control of access to the call completion on busy link service in a private telecommunication network

ABSTRACT

In private telecommunication networks offering a call completion on busy link service, if a call request cannot be completed because of congestion of a link, and if setting up the call entails an overflow to the public network, the rights of the user may not be sufficient for subsequent completion of the call. To prevent this service being offered to a user whose rights are insufficient to enable subsequent call completion, because of the overflow, costs are assigned to the various links of the private network as a function of the overflows and access to the call completion on busy link service is monitored as a function of the rights of the user and the minimum total cost of completing the requested call. This prevents users with insufficient rights being queued indefinitely waiting for the call completion on busy link service.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention is a method of controlling access to thecall completion on busy link service in a private telecommunicationnetwork.

[0003] 2. Description of the Prior Art

[0004] The invention concerns private telecommunication networks. Suchnetworks are formed of communication nodes connected together by linkscarrying calls and/or signaling. It applies equally to physical privatenetworks (which are formed of dedicated connections), virtual privatenetworks and hybrid networks combining the two solutions. In theremainder of the description the invention is described with referenceto one example of a private network with signaling, but it applies moregenerally to other private networks.

[0005] The Dijkstra algorithm is described in the literature onalgorithms and calculates the shortest path between two nodes in agraph. The algorithm operates as follows: it considers a graph G with Nnodes, which is valued, i.e. each existing path of which between twonodes i and j is assigned a value or weight l(i, j). it considers anoutgoing node s of the graph G and an incoming node d; it seeks a pathminimizing π(s, d), the distance from s to d, i.e. the sum of the valuesof the connections connecting s to d. S is the subgraph of G formed ofthe nodes x for which the minimum path to s is known, and {overscore(S)} is its complement. Γ_(i) is the set of nodes adjoining a given nodei.

[0006] Initially the subgraph S contains only the node s, and {overscore(S)} contains all the other nodes, assigned the following initialvalues:

[0007] π(s, i)=l(s, i) for i ∈Γ_(s), the parent node being s;

[0008] π(s, d)=∞, for the other nodes, which have no parent node.

[0009] An iteration of the algorithm is effected in the followingmanner.

[0010] If {overscore (S)} is empty, or if it contains only nodes i withπ(s, i)=∞, the algorithm has finished.

[0011] Otherwise, the node n of {overscore (S)} is considered which isnearest the originating node, i.e. the node which minimizes π(s, i), i ∈{overscore (S)}; this node is taken from {overscore (S)} and placed inS.

[0012] The nodes adjacent this node n are then considered and thealgorithm calculates

π(s, n)=l(n, j),j∈Γ _(n) and j∈{overscore (S)};

[0013] If this quantity is less than π(s, j), then π(s, j) is updated:

π(s, j):=π(s, n)+l(n, j)

[0014] and the parent node of is also updated, which becomes n.

[0015] This operation is carried out for all the nodes of Γ_(n), afterwhich {overscore (S)} is reordered.

[0016] In this way, all the nodes of the graph are progressively addedto S, in order of increasing path length. To find a path to a given noded, the algorithm can be interrupted before it finishes, since thedestination node a has been added to the subgraph S.

[0017] The validity of the algorithm is demonstrated by the followingreductio ad absurdum argument. Consider the node n nearest {overscore(S)} which must be added to S. If there is a nearer path, that pathstarts from s and arrives at n and has a first node m in {overscore(S)}. Then:

π(s, m)+π(m, n)<π(s, n)

[0018] and, since π(m, n) is positive or zero:

π(s, m)<p(s, n)

[0019] which contradicts the hypothesis. It is also clear that π(s, m)has been calculated in a preceding iteration, when adding the parent ofm to S.

[0020] The document by J. Eldin and K. P. Lathia “Le RNIS appliqué auCentrex et au réseaux privés virtuels” [The ISDN applied to Centrex andto virtual private networks] contains a description of physical privatenetworks and virtual private networks. As explained in the document, ina physical private network the various sites or nodes are connected bydedicated circuits but in a virtual private network each node isconnected to the local switch nearest the public network, whereappropriate software sets up the connections on demand. There are twovariants of the virtual private network: on the one hand, semi-permanentconnections can be provided, which are set up without dialing as soon asany of the nodes requires the circuit, and which always connect the sametwo points. Such may be the case in particular for signaling connectionsin an application on an integrated services digital network. On theother hand, switched connections can be provided, which can be set uponly by dialing.

[0021] The remainder of the description considers only physical orvirtual private networks formed of nodes connected by links, which canbe of any type: dedicated connections, or links using an externalnetwork; the latter can be of any type—the public switched network, apublic land mobile network, an integrated services digital network, etc.FIG. 1 shows one example of a private network of this kind. This networkincludes, for example, nodes 1 to 6; nodes 1, 2 and 4 to 6 are connectedto the public network 8 by circuit groups 11, 12 and 14 to 16. The nodesare interconnected by links formed of private connections, shown in boldin the figure, or, as in the case of the link between nodes 5 and 6, bya link comprising only a signaling connection. For a digital link, eachprivate connection comprises at least one access, formed by a signalingconnection and a plurality of B channels. The link between nodes 5 and 6in FIG. 1, and likewise the link between nodes 1 and 2, comprises asignaling connection and no B channel; this is typical of a nodecorresponding to a branch office, for which the volume of traffic is notvery high.

[0022] The problem of overflow, i.e. the problem of a call request thatcannot be satisfied by the network because its resources are congested,arises in private networks. This problem can arise if the private linksof the private network have a fixed capacity, rather than a capacitywhich is allocated dynamically and which is less than the possiblemaximum volume of traffic. Completing the corresponding call using thepublic network is known in itself. In other words, if a user at node 2wants to contact a user at node 6, and if the private network iscongested and cannot complete the call, the call is completed viacircuit groups 12 and 16 and the public network. This can be the case,for example, if the connection between nodes 2 and 4 is congested. InFIG. 1, reference numeral 10 shows schematically a call of this kind viathe public network. Overflow may also be necessary if the link inquestion has no B channel, as in the case of node 6 in FIG. 1.

[0023] One problem is the cost of such overflows. Because of this cost,rules can be defined denying certain users or certain categories of useraccess to this service.

[0024] The prior art also provides a CCBL (call completion on busy link)service which provides automatic callback if a link of the privatenetwork is busy or congested. In this case, the calling user is put onhold for as long as the private network link is congested and is calledback when sufficient resources are released to route the call. Inexisting private networks this CCBL service is provided withoutdistinguishing between users.

[0025] This solution gives rise to the following problem in the case ofoverflows to the public network. If an overflow is necessary to reachthe called user, and if the rights or monitored cost of the user areless than the charge incurred for the overflow, the CCBL service mightnever call back. This is the case in particular for users who have nooverflow rights. The CCBL request therefore remains unsatisfied.

[0026] The invention proposes a solution to this new problem. Itprevents users being queued unnecessarily and prevents congestion of theprivate network by CCBL requests that cannot be satisfied. The inventionapplies particularly to the routing solution proposed in our applicationfiled the same day as this application with the title “Routing of callswith overflow in a private network”. It also applies to routes chosen bya separate process and which enables one or more overflows to a publicnetwork.

SUMMARY OF THE INVENTION

[0027] To this end, the invention proposes a method of controllingaccess to the call completion on busy link service in a privatetelecommunication network allowing overflow to another network, whereinusers are allocated rights to overflows and access to the service by auser for a call entailing at least one overflow is dependent on therights of the user.

[0028] In one embodiment of the method some users do not have the rightto overflows and access to the service for a call entailing at least oneoverflow is refused to such users.

[0029] A step of calculating the minimum number of overflows for a callcan be provided, advantageously using the Dijkstra algorithm.

[0030] In one embodiment of the method certain links are not monitored,certain users do not have rights to overflows except on said links whichare not monitored and access to the service for a call entailing atleast one overflow onto an unmonitored link is refused to such users.

[0031] A step of calculating the minimum number of overflows ontomonitored links for a call can be provided, advantageously using theDijkstra algorithm.

[0032] In another embodiment of the invention access to the service by auser for a call entailing at least one overflow depends on a comparisonof the rights of the user and the cost of the overflow(s).

[0033] The method preferably comprises a step of calculating the minimumcost of the overflows for a call, preferably using the Dijkstraalgorithm.

[0034] A connectivity flag can then be propagated during application ofthe Dijkstra algorithm to determine if there is a path withoutoverflows.

[0035] Other features and advantages of the invention will becomeapparent on reading the following description of embodiments of theinvention, which is given by way of example and with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 is a diagrammatic representation of a prior art privatenetwork.

[0037]FIG. 2 is a diagrammatic representation of a private network inwhich the invention is used.

[0038] FIGS. 3 to 6 are flowcharts of various embodiments of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] The invention proposes, in a virtual private network, todetermine the minimum cost of a call, in terms of overflows, to enableefficient management of the CCBL service as a function of the rights ofcalling users.

[0040] To this end, the invention proposes to assign to each link of theprivate network a valuation or cost, denoted CCBLCost hereinafter,reflecting the fact that an overflow is necessary or not necessary toroute a call between the two nodes connected by that link. FIG. 2 is adiagrammatic representation of a private network, similar to that fromFIG. 1; FIG. 2 show the number of channels on each link, and thecorresponding CCBLCost. The latter can be determined in the followingmanner:

[0041] for links allowing routing of calls, the cost is zero;

[0042] for links necessarily involving an overflow, the cost isnon-zero.

[0043] Accordingly, in the FIG. 2 embodiment, the CCBLCost is zero forthe links between nodes 1 and 3, 2 and 4, 4 and 5. In fact, each ofthese links has at least one B channel and therefore can route callswithout overflow onto the public network.

[0044] The CCBLCost of the links between nodes 1 and 2, on the one hand,and between nodes 5 and 6, on the other hand, is non-zero. In fact,these links have no B channel, but only a signaling channel, andoverflow is therefore essential for routing a call.

[0045] The invention therefore makes it easy to determine whetheroverflow is needed or not for a call request and to grant or refuse theCCBL service. For this it is sufficient, for a given call request, tosum the CCBLCost values of the links that the requested call must use;the minimum cost of the call is obtained in this way.

[0046] For example, between nodes 2 and 5, a call can be set up via node4 and links of the private network which each have at least one Bchannel. The cumulative CCBL cost of the various links is thereforezero, and this is representative of the fact that a call can be set upwithout overflow.

[0047] Between nodes 4 and 6, for example, or between nodes 2 and 6, acall can be set up only using overflow via the public network. Theoverflow can be direct overflow, as in the prior art, using a call viathe public network between nodes 4 and 6, for example. As explained inour patent application referred to above, the overflow can also be anoverflow between nodes 5 and 6, the call passing between nodes 4 and 5in the private network.

[0048] In all cases, a call between these nodes necessarily uses a linkof the private network whose CCBLCost is non-zero. This isrepresentative of the fact that a call cannot be set up without at leastone overflow.

[0049] In this embodiment, the valuation or the cost of the links havingonly a signaling channel can have any non-zero value; a value of 1 issuitable, for example. The invention enables the CCBL service to berefused to a user who has no overflow rights if the call envisagednecessarily entails an overflow. In this case the invention functions inthe following manner. In the case of a call set-up request, if a link isbusy, and if the CCBL service is required, the algorithm determines:

[0050] if the user has the overflow right, and

[0051] if there is a possible route without overflow.

[0052] If the user has no overflow right, and if there is no possibleroute for the requested call, the CCBL service is refused. This avoidsqueuing users unnecessarily.

[0053] To determine whether a call for which the CCBL service isrequired entails an overflow or not, the invention proposes to calculatethe shortest path across the private network, treating the CCBLCost asdefined above as a distance. It is therefore possible to determine theminimum cost in terms of overflows for a given call, in order to refuseor to grant the CCBL service. In other words, with the valuation choicesdefined above, a shortest path calculation is effected:

[0054] if the shortest path has a zero total valuation, there is a routewithout overflow;

[0055] if the shortest path has a non-zero total valuation, there is noroute without overflow.

[0056] The shortest path calculation can advantageously be effectedusing the Dijkstra algorithm. The algorithm can be applied to theinvention by considering the graph formed of the nodes of the privatenetwork, the links between the nodes being valued by the CCBLCostdefined above. The minimum path for a call, in terms of the cumulativeCCBLCost on the links of the private network, is obtained in this way ina time period O(n2).

[0057] Other methods could also be used to determine if there is a routewithout overflow; as in the second embodiment, one solution consists inpropagating a flag representative of the connectivity between thecurrent node and the originating node when applying the Dijkstraalgorithm.

[0058] The invention applies in this first embodiment, and refuses theCCBL service to users who have no overflow rights. Referring to FIG. 2,for example, a user at node 1 may want to call a user at node 4. Theshortest path in the private network, in terms of the CCBLCostvaluation, is a non-zero distance: in fact, because node 1 is connectedto the part of the private network containing node 4 only via the linkbetween the nodes 1 and 2, which has no B channel, a call to a user atnode 4 entails an overflow, at least onto the link between nodes 1 and2. In this case, as explained above, if a user has no right to anoverflow, a CCBL request granted to that user might never be satisfied.In this situation the invention proposes to refuse the CCBL service tothe user.

[0059] Another embodiment of the invention will now be described; inthis embodiment, the invention proposes to grant the CCBL service or notas a function of the rights of the user and the cost of the overflowsneeded to route the call. This embodiment of the invention allocatesusers rights that can take more than two values, i.e. that are no longerbinary.

[0060] In this embodiment, the valuation or the cost of the links havingonly a signaling channel has a non-zero value which is made equal to theoverflow cost. In this way not only can the CCBL service be refused tousers who do not have overflow rights, but also the CCBL service can beprovided or not to users having given rights, as a function of the costof the call for which the CCBL service is requested. In FIG. 2, theCCBLCost between nodes 1 and 2 is 2, which reflects the cost of theoverflow between these nodes; the overflow can be via circuit groups 11and 12; the CCBLCost between nodes 5 and 6 is 3, for an overflow viacircuit groups 15 and 16. This example considers the minimum cost thatcorresponds to overflow via the nearest circuit groups. Depending on thenature of the public network and the circuit groups, the minimum costcan correspond to these overflows via circuit groups other than thenearest circuit groups.

[0061] In this embodiment, it is also possible to allocate a zerovaluation to a link for which an overflow is mandatory. In this way azero valuation can be allocated to a link having no transmission paths,which amounts to authorizing overflow to that link independently of therights of users. This corresponds to a choice of the networkadministrator whether or not to monitor overflows onto a given link.

[0062] This second embodiment of the invention compares the rights of auser with the cumulative cost of the overflows. In this case, each useris allocated rights or monitored costs representative of the maximumcharge that can be incurred for overflows. At the time of a request, theCCBL service is granted or refused according to the result of comparingthese rights to the minimum cost of the call for which the CCBL serviceis required. In a configuration of this kind, the rights of a user canbe defined in the following manner:

[0063] −1 if the user has no right to overflow to the public network;

[0064] 0 if the user has a right to overflow only if the links cannotroute calls, i.e. if the links do not have any B channels, in thisexample;

[0065] n, 1=n=max if the user has a right to overflow(s) to the publicnetwork, to the extent that the cumulative charges are less than orequal to n, “max” being a higher value for which there are no limits onthe rights of the user.

[0066] In this example of definition of the rights of users, for a userwith “−1” rights the situation is as described above with reference tothe first embodiment. A user of this kind cannot obtain a CCBL serviceentailing overflows; this can be the case for long calls, for exampledata transfers. This definition of rights with a value “-1” is used todistinguish users for whom an overflow is never possible, even for linkswithout transmission paths having a zero valuation.

[0067] A user with “0” rights can obtain a CCBL service on a routingwithout overflow or on a routing with overflows onto links that are notmonitored, i.e. onto links with no transmission paths whose valuation iszero.

[0068] A user with rights n, 1=n=max can obtain the CCBL service for acall involving overflows with a total cost less than n.

[0069] The Dijkstra algorithm can again be used in this embodiment ofthe invention to determine the minimum cost of a route, in order togrant the CCBL service or not. At the same time it is possible todetermine if there is a route without overflow by propagating a flagrepresentative of the connectivity with the source node via the Bchannels. Then, during iterations of the Dijkstra algorithm, it ispossible to use a flag BchConn(i) representative of the connectivity ofthe node i with the originating node via links with B channels. Thisprovides a simple way of determining if there is a route withoutoverflows.

[0070] BchConn(i) is initialized to the value “false” for all idifferent from s. With the same notation as above, consider n a node andΓ_(n) its vicinity, the node n being at a given time the summit of thesubgraph {overscore (S)}. For any node v in the vicinity, the algorithmdetermines whether there is a B channel between the node n and the nodev. If there is such a channel—which can be declared on initializing thenetwork—the flag BchConn(v) is updated to the value “true” if the flagBchConn(n) is true. In other words, if the node v is connected to thenode s by B channels, and if the link between n and v also includes a Bchannel, the node b is connected to the node s by n channels.

[0071] If the node n is not connected to the node s, or if there is no Bchannel between the node n and the node v, the flag of the node v isleft at its current value. When the Dijkstra algorithm calculates ashorter path, this solution determines the existence of a route withoutoverflows; if there are none, this avoids queuing users having “−1”rights unnecessarily.

[0072] A CCBLCost defined as follows can be used to value the links. Ifthe link between the node n and the node v has at least one B channel,the CCBLCost of the link is considered to be zero. If there is no Bchannel between the node n and the node v, the algorithm verifies ifthere is an overflow. If so, the algorithm determines if the linkbetween n and v is monitored. If not, the CCBLCost is zero. In contrast,if the link is monitored, then the CCBLCost is equal to the overflowcost. On the other hand, if there is no overflow, the CCBLCost of thelink is infinite. Thus a CCBLCost is defined with the following values:

[0073] 0 for links having a B channel, or for links that are notmonitored;

[0074] the cost of the overflow for monitored links without B channels;

[0075] infinity for links with no B channels for which overflow is notpossible.

[0076] Choosing this cost function enables the overflow cost to bemonitored as a function of the rights of the user. Furthermore, thepropagation in the algorithm of a flag representative of theconnectivity with the source via B channels means that the service canbe refused to users who have no right to overflow.

[0077]FIG. 3 is a flowchart of one embodiment of the invention for onesuch type of definition of user rights; the FIG. 3 embodiment considersnot only overflows of the type described above, but also singleoverflows to the public network. In the former case, referred to alsohereinafter as overflows to a “virtual private network”, the overflow istransparent for the private network user; the signaling is routed viathe private network and the overflow compensates for the absence orcongestion of B channels. In the latter case, the overflow amounts tosupplying the user with only the services of the public network, theservices specific to the private network being lost.

[0078] Step 20 corresponds to a call set-up request by a given user ofthe private network. In step 21, the algorithm determines if the callcan be routed in the private network without overflow. If it can, thealgorithm moves on to step 22 and the connection is set up via theprivate network without overflows. If not, the algorithm moves on tostep 23.

[0079] In step 23, routing without overflow is impossible; the status ofthe link(s) for which an overflow is necessary is determined; if a linkis down, the algorithm moves on to step 24, otherwise it moves on tostep 25. This step is not mandatory, but it has the advantage ofenabling different treatment of calls when a portion of the privatenetwork is down.

[0080] In step 24, a link is known to be down. In this case noconnection providing the services of the private network can beprovided. The algorithm determines if a single overflow is authorized inthis case of a link being down. This in fact represents a parametersetting of the private network by the operator. If it is not authorized,there is congestion, the algorithm moves on to step 25, and the CCBLservice is refused.

[0081] If it is authorized, on the other hand, the algorithm moves on tostep 32. In step 32 the call is routed with a single overflow, i.e.providing only the services of the public network.

[0082] In step 25, it is known that the overflow is imposed bycongestion of the channels of at least one link; the rights of thecalling user are determined. If the rights of the user are “−1”, i.e. ifthe user never has the right to an overflow, the algorithm moves on tostep 26. Otherwise it moves on to step 27.

[0083] Step 27 determines whether the call can be routed with one ormore overflows; if so, the algorithm moves on to step 28 and if not tostep 26.

[0084] Step 28 compares the routing cost with overflow to the rights ofthe user. If the rights of the user are less than the cost of routingthe call, the algorithm moves on to step 26; otherwise it moves on tostep 29.

[0085] In step 29 the call is routed with one or more overflows to thepublic network (virtual private network). In this case, it is notnecessary to provide any CCBL service. As explained above, the servicesof the network are supplied and the overflow(s) are transparent for theuser.

[0086] In step 26, the situation is that one of the links for setting upthe connection is congested and an overflow preserving the services ofthe private network has not been allowed because of the limitation onthe rights of the user. The algorithm determines if the user has theright to a single overflow in the case of a busy link. If so, thealgorithm moves on to step 32 in which the call is routed with a singleoverflow (see above).

[0087] If not, the algorithm moves on to step 30. It determines if theuser has a right to the CCBL service. If so, it moves on to step 31; ifnot, it moves on to step 35. In step 35 there is congestion (see above).

[0088] Step 31 determines if there is a possible route across theprivate network using only the links of the private network. This cansimply be done by the shortest path calculation mentioned with regard tothe first embodiment, with a non-zero valuation for all the links withno transmission paths. This can also be effected by propagating a flagin the shortest path calculation using the Dijkstra algorithm.

[0089] If this is the case, the algorithm moves on to step 34 in whichthe CCBL service is provided.

[0090] If not, it moves on to step 33. In step 33 it determines if therights of the user are less than or equal to the total cost of theminimum routing, i.e. to the lowest CCBLCost for the requestedconnection. Once again, this comparison is advantageously effected usingthe Dijkstra algorithm (see above).

[0091] If the rights of the user are less than or equal to the totalcost of the minimum routing, the algorithm moves on to step 35. There iscongestion.

[0092] If the rights of the user are greater than the total cost of theminimum routing the algorithm moves on to step 34, in which the CCBLservice is provided.

[0093] In this way, the CCBL service is always refused if the user doesnot have sufficient rights, which prevents the user from being queuedindefinitely. Accordingly, assuming that the links are in service (nolink down in step 23):

[0094] a user having no overflow rights preserving the services of thenetwork or single overflow rights is provided with the CCBL service onlyif there is a possible route across the private network (steps 25, 26,30, 31 and 34);

[0095] a user having rights to overflow preserving the services of thenetwork is provided with the CCBL service only if there is a possibleroute across the private network whose cost is compatible, and less thanthe user's rights (steps 25, 26, 30, 31, 33 and 34).

[0096] Note that the FIG. 3 flowchart is compatible with the variousmodes of valuation of the overflows mentioned above. A zero CCBLCost canbe given to a link with no B channels, or not, without this modifyingthe process described with reference to FIG. 3.

[0097]FIG. 4 is a flowchart of another embodiment of the invention; theFIG. 4 flowchart is suited to the first embodiment mentioned above,where it was simply a question of refusing the CCBL service if the userhas no right to it. The FIG. 4 flowchart is similar to that from FIG. 3,subject to the following modifications:

[0098] step 28 is eliminated, and so where appropriate the algorithmgoes directly from step 27 to step 29;

[0099] step 33 is eliminated, and so the algorithm goes directly fromstep 31 to step 35 if there is no possible route within the privatenetwork.

[0100] The FIG. 4 embodiment merely:

[0101] refuses the CCBL service for certain categories of user having noright to overflow if there is no possible route in the private network;

[0102] grants the CCBL service otherwise, independently of the cost ofthe overflow.

[0103]FIGS. 5 and 6 are flowcharts of further embodiments of theinvention; these figures correspond to situations in which singleoverflow is not provided.

[0104] The FIG. 5 flowchart is similar to that from FIG. 3, subject tothe following modifications:

[0105] step 24 is eliminated, and so where applicable the algorithm goesdirectly from step 23 to step 35;

[0106] step 26 is eliminated, and so the algorithm goes directly fromstep 25, 27 or 28 to step 30.

[0107] The FIG. 6 flowchart is similar to that from FIG. 4, subject tothe following modifications:

[0108] step 24 is eliminated, and so where applicable the algorithm goesdirectly from step 23 to step 35;

[0109] step 26 is eliminated, and so the algorithm goes directly fromstep 25 or 27 to step 30.

[0110] Operation in accordance with the FIGS. 5 and 6 flowcharts isrespectively similar to that in accordance with the FIGS. 3 and 4flowcharts, except that no single overflow is provided.

[0111] All embodiments of the invention can manage the CCBL service insuch a way as to avoid indefinitely queuing a user whose rights are notsufficient to enable subsequent routing of the call.

[0112] Of course, the present invention is not limited to theembodiments and examples described and shown, but is open to manyvariants that will suggest themselves to the skilled person. It appliesto private network types other than those described above. It alsoapplies to other types of overflow than those described in ouraforementioned application entitled “Routing of calls with overflow in aprivate network”. The terms “overflow”, “private” and “public” have beenused in the above description; the invention applies equally to overflowto different public networks, such as the public switched network,public land mobile networks or public satellite mobile networks and/oroverflows to other private networks.

[0113] In the second embodiment described above, it is possible not todefine users with “−1” rights; in this case, compared to the descriptionof FIG. 3, no distinction is drawn between:

[0114] a link with a zero valuation, because it has transmissionchannels;

[0115] a link with a zero valuation although it does not havetransmission channels, i.e. a link that is not monitored.

[0116] What is more, allocating a CCBL cost to the links of the privatenetwork can also be used for other applications.

[0117] Finally, the description and the claims mention the Dijkstraalgorithm. It is to be understood that this term covers not only theversion of the shortest path algorithm proposed by Dijkstra, but alsosimilar versions, and in particular the Bellman algorithm or the Floydalgorithm. Note that the Bellman algorithm applies only to graphswithout circuits.

There is claimed:
 1. A method of controlling access to the callcompletion on busy link service in a private telecommunication networkallowing overflow to another network, wherein users are allocated rightsto overflows and access to said service by a user for a call entailingat least one overflow is dependent on said rights of said user.
 2. Themethod claimed in claim 1 wherein some users do not have said rights tooverflows and access to said service for a call entailing at least oneoverflow is refused to such users.
 3. A method as claimed in claim 2comprising a step of calculating the minimum number of overflows for acall.
 4. The method claimed in claim 3 wherein said calculation stepuses the Dijkstra algorithm.
 5. The method claimed in claim 1 whereincertain links are not monitored, certain users do not have rights tooverflows except on said links which are not monitored and access tosaid service for a call entailing at least one overflow onto anunmonitored link is refused to such users.
 6. A method as claimed inclaim 5 including a step of calculating the minimum number of overflowsonto monitored links for a call.
 7. The method claimed in claim 6wherein said calculation step uses the Dijkstra algorithm.
 8. The methodclaimed in claim 1 wherein access to said service by a user for a callentailing at least one overflow depends on a comparison of said rightsof said user and the cost of said overflow(s).
 9. A method as claimed inclaim 8 comprising a step of calculating the minimum cost of theoverflows for a call, preferably using the Dijkstra algorithm.
 10. Amethod as claimed in claim 9 wherein a connectivity flag is propagatedduring application of the Dijkstra algorithm to determine if there is apath without overflows.